PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 87 
On 1° gramme— 
Silica, . A : 356 
From Alumina, . . 004 
* 360 = 36° 
Ferric Oxide, . ; . 22°8 
Ferrous Oxide, . ‘ . 2°462 
Manganous Oxide, . : °5 
Lime, : ‘ : ee ee ae 
Magnesia, . : : , oe 
Alkalies, . : : . trace 
Water, : : : . 26°463 
100 : 254 
Loses 19°227 of the above water at 212°. It was rapidly and perfectly 
dissolved in chlorhydric acid. 
2. The decomposed auneral.—Dr MaccutLocy was unable to ascertain the 
nature of the circlet of cliff which, like an Elizabethan collar, girdles the top of 
the Scuir. He supposed it to be imaccessible. It can, however, be easily 
| turned at its north-west corner by approaching it from the landward side, and 
_ is then found to consist from top to bottom of repeatedly alternating bands of 
| basalt and of amygdaloid. 
The basalt is in rudely columnar forms, and contains very sparsely distributed 
| amygdules of the chlorophzite, of about half the size of an almond, Its beds are 
| six to eight feet in thickness. 
The amygdaloidal beds are little over a foot in depth. This is a more 
| vesicular rock than I ever saw even in Farde. There has been very much more 
| of steam-hole cavity than of solid material; the amygdules are of about the 
| size of swan-shot, and they almost coalesce with each other on all sides. They 
are for the most part plugged with decomposed chloropheite and chalcedony ; 
| those on the surface being empty, from the nodules having dropped from their 
| casts,—which nodules may be gathered almost in handfuls at the foot of the 
| cliff. 
| I worked into this amygdaloidal bed as far as seemed safe under the over- 
hanging and by no means firmly attached columns, but did not reach to a part 
of the rock where the chloropheite was fresh, and had therefore to content 
| myself with analysing the altered mineral. 
Its colour is rich chocolate brown, it is friable and very soft, having all the 
| appearance of being altered; and as the chloropheite of the dense basalt may, 
| when exposed or within an inch of the surface of the rock, be seen to pass into 
| the ochreous variety, there can be little doubt that the mineral is the same. 
ee VOL. XXIX, PARP I. Z 
